The present invention relates to a backing plate and its manufacturing process for producing a sputtering target to be used in a sputtering process. The invention relates to a welding process of a Ti material which welds with high reliability and strength a titanium (hereafter referred to as Ti) material to be used suitably for the backing plate or the like.
Sputtering is a well-known process for forming a thin film on an integrated circuit or the like. A sputtering target is used in processes of physical sputtering (PVD) and reactive sputtering. The sputtering target is composed of a target member upon which ions are impacted, and a backing plate at its rear for supporting the target member. Cooling channels between the target member and the backing plate generally carry liquid coolant to keep the operating temperature of the target within an operating range. Concretely, it is known that a specified metallic material target member is soldered to the backing plate made of a Ti material. For example, it is disclosed in Japanese Patent Application Laid Open No. 6-293963 that Ti material is used in the backing plate.
FIG. 12 is an exploded sectional view showing a conventional backing plate. The backing plate is composed of a substrate 21 for supporting a target member on one surface, and a cover member 22 to be affixed on the other surface of the substrate 21. The cover member 22 has groove notches 23 machined in advance on the side of the joining face to be soldered to the other surface of the substrate 21. A space defined by the grooves 23 and the facing surface of the substrate 21 forms channels for cooling water after welding of the cover member 22 to the substrate 21. The described configuration is called water-cooled jacket construction. A backing plate of the water-cooled jacket construction is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-197248. The groove for forming the water channel machined in advance is disclosed in, for example Japanese Patent Application Laid-Open No. 5-132774.
Referring now also to FIG. 13, the joint between the cover member and the substrate 21 may be silver soldered using silver solder 24 (Japanese Patent Application Laid-Open No. 5 132774, Japanese Patent Application Laid-Open No. 3-140464).
Other methods of affixing the cover member 22 to the substrate include bolting, high-energy beam welding (Japanese Patent Application laid-Open No. 7-197248) using, for example, EBW (electron beam welding), and LBW (laser beam welding), or other conventional welding or joining processes.
In order to manufacture the backing plate with silver solder, the sealing area must be substantially larger, because the strength of silver solder is lower than that of base metal. The increased welding area requires that the backing plate must be larger in size.
If the cover member 22 is bolted to the substrate, an increased thickness is required to accommodate a screw portion in the backing plate to obtain a sufficient strength. This increases the backing plate thickness.
When the backing plate is manufactured with high energy beam welding, the specified welding strength is possible because the strength of the welded joint is almost the same as that of the base metal. But, since welding is not conducted between the facing surfaces, the possible shapes available for fabrication of the backing plate and the water channel are limited.
Machining costs for forming the groove portion 23 for the water channel in the cover member 22 increase the cost of the product.
Accordingly, an object of this invention is to provide a backing plate and its manufacturing process which can weld a plurality of components of Ti material with high reliability and strength.
It is a further object of the invention to provide a backing plate that is thinner and increases the degree of freedom of shape in the construction.
Another object of this invention is to provide a Ti material welding process which can be used preferably for manufacturing the backing plate and can weld the Ti material with high reliability and strength.
In a manufacturing process of a backing plate composed of a plurality of components, made of the Ti material, welded together, a manufacturing process of a backing plate comprises the steps of interposing a copper (hereinafter referred to as Cu) material on the welding face of the components, heating the material to a welding temperature selected to an eutectic temperature or more of Tixe2x80x94Cu alloy, or preferably a decomposition temperature or more of an intermetallic compound to be formed by both of the materials so as to produce a liquid phase of the Cu material. The welding temperature is maintained long enough to permit the Cu material to diffuse sufficiently in the Ti material.
Briefly stated, the present invention provides a backing plate of Ti for supporting a Ti sputtering target. The backing plate is formed of at least two components by interposing a Cu or Zr foil or powder between faces to be welded, and then heating the assembly to a reaction temperature high enough to melt one of the Ti and Cu or Zr to produce a liquid phase. The heating is retained for a time long enough to permit diffusion of the Cu or Zr into the Ti to produce a liquid phase diffusion weld. By permitting diffusion to occur, a separate metallic compound is not produced at the welding face. In effect welding is accomplished without producing a welding face, whereby no interface exists in the finished weld. The resulting weld has a strength substantially equal to the strength of the Ti material, and very good welding qualities.
According to an embodiment of the invention, there is provided a process for joining at least two components of Ti material comprising: interposing a Cu material on a welding face between the two components, heating the two components and the Cu material to a welding temperature at which the Cu material is liquified, maintaining the welding temperature for a sufficient time to permit a substantial diffusion of the Cu material into the two components, and the substantial diffusion being sufficient to substantially remove liquid Cu material from the welding face by the diffusion of the Cu into the Ti material.
According to a feature of the invention, there is provided a process for joining at least two components of Ti material comprising: interposing a Zr material on a welding face between the two components, heating the two components and the Zr material to a welding temperature at which the Zr material is liquified, maintaining the welding temperature for a sufficient time to permit a substantial diffusion of the Zr material into the two components, and the substantial diffusion being sufficient to substantially remove liquid Zr material from the welding face by the diffusion of the Zr into the Ti material.
According to a further feature of the invention, there is provided a process for welding first and second components of Ti materials at a welding face comprising: interposing a layer of a second metallic material between the first and second Ti materials at the welding face, the second metallic material being of a type capable of diffusion into Ti materials at a reaction temperature, heating the first and second components and the second metallic material to the reaction temperature, and maintaining the reaction temperature for a sufficient time to permit a diffusion of the second material into the Ti material until substantially none of the second material remains between the first and second components.
According to a still further feature of the invention, there is provided a backing plate comprising: at least first and second components, the first and second components being of a Ti material, a first welding face on the first component, a second welding face on the second component, the first and second welding faces being welded to each other to form a weld between the first and second welding faces, and the weld including a second metallic material diffused though the first and second welding faces, and leaving substantially none of the second material between the first and second welding faces.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.